You should not be worried about color of the blood during periods. You should look for the duration of the periods and timings of the periods. If you are getting periods before 21 days gap then visit a doctor to find out exact cause of this problem. Following are some common causes of this condition.
- Malnutrition
- Hyperactivity of pituitary gland causing frequent ovulation
- Pelvic inflammatory disease
- Stress
- Hormonal imbalance